High-frequency inductance unit



Feb. 6, 1945. B, MccLELLAN 2,368,857

4 HIGH-FREQUENCY INDUCTANGE UNIT Filed June 24, 1943 2 Sheets-Sheet 1 0 I l V GEORGE B. MCCL BY Mmf. 6m

Patented Feb. 6, 1945 HIGH-FREQUENCY INDUCTANCE UNIT George B. McClellan. Chicago, EL, assignor to Johnson Laboratories poratlon oi Illinois Inc., Chicago, Ill; a cor- Application June 24, 1943, Serial No. 492,086

Claims.

This invention is an inductance unit for use in regulating and/or controlling alternating current circuits, more particularly high frequency signal circuits such as used in connection with radio transmitters and receivers.

Considerable difilculty has been experienced in the past in simultaneously tuning matched or balanced brauch circuits oi a radio frequency network connected between the end terminals and the center tap connection of a straight or conventionally wound solenoid having a movable core member, due to the shifting of the electrical center of the solenoid relatively to the center tap connection as the core member is entered and moved within the coil from one end. ihis relative shifting of the electrical center oi the solenoid under the'conditions noted manifests itself in several ways, namely: by a relative change in the grid currents of the tubes included in the respective branch circuits; by unequal ratios of loaded to unloaded plate currents for the respective tubes in push-pull systems; and in uneven heating of the tube electrodes. Furthermore, the relative shifting of the electrical center of the solenoid may be verified by measuring the inductances of the respective coil sections on opposite sides of the center tap un-- der the conditions noted, whereby it can be shown that the inductance values of the two coil sections diiler appreciably. These conditions are seriously objectionable in that they prevent that uniformity of intensity of oscillation of the tubesv which is essential to efilcient operation and control. Numerous attempts have been made to avoid these diiliculties, such as by employing separate core members movable into the coil from opposite ends, but so far as is known. these prior attempts have all required more or less complicated electrical or mechanical devices for relatively moving the core members with respect tothe coil sections to insure symmetrical tuning of the branch circuits simultaneously.

The object of the invention therefore, is to provide an inductance unit having plural coil sections so positioned that a single core member may be moved axially of the unit to simultaneously vary the inductance values of the coil sections.

Another object of the invention is to provide an inductance unit which may be symmetrically connected in respect to substantially identical branch circuits in networks where it is desirable to simultaneously tune two branch circuits to the same, or substantially the same resonant frequency while maintaining the mid-point or center tap connection between said unit and circuits substantially coincident with the electrical center of the inductance unit.

Another object of the invention is to provide an inductance unit in which are provided plural coil sections arranged to provide coincident magnetic fields so that a single core member may be moved by simple mechanical means, in said fields to simultaneously vary" the inductances of the coil sections to thereby simultaneously vary the electrical characteristics of the branch circuits connected to said coil sections.

Another object of the invention is to provide an inductance unit in the form of a bifllar winding, the two strands or wires forming said bifilar winding having their ends connected so as to form a continuous winding having a center tap connection, the coil sections on opposite sides of said center tap being disposed to provide coincident magnetic fields.

Another object of the invention is to provide an inductance unit of the character "described in which a powdered iron core member may be moved in the coincident magnetic fields pro vided by the coil sections of the unit, whereby the unit may be used in what is generally known as permeability tuning systems for radio frequency signal circuits.

A further and important object of the invention is to accomplish the previously recited objectives without materially changing the distributed capacity of the unit.

These and other objects of the invention will become apparent from reading the following specification in connection with the accompanying drawings wherein I have described and illus trated preferred embodiments of my invention. It will be understood, however, that I may make such changes in size and proportion of parts and in-the relative arrangements thereof as are within the scope of the appended claims without departing from the spirit of my invention.

Referring to the accompany drawings Fig. 1 shows in front elevation one iorm oi the inductance unit.

Figs. 2, 3 and 4 are diagrammatic views illustrating the manner in which the coil sections of the inductance units may be mounted upon or wound on the coil forms.

Fig. 5 is a detail view of one form of the coil form or support.

Figs. 6, 7, 8 and 9 are circuit diagrams illustrating representative forms of networks including tunable branch circuits in which the present invention may be employed.

Fig. 10 is a chart showing effects produced by differently connecting the sections of a two section inductance unit in accordance with the invention.

Referring more articularly to the drawings in which like reference numerals are used to desi nate like parts throughout, the inductance unit forming the subject matter oi! the present invention is shown in Fig. 1 as comprising a suitable base member i on which is mounted a coil form or support 2. The coilsupport 2 may be mounted upon the base in any convenient manner such as by bracket members 3-3. Preferably, but not necessarily, the coil form or support I is mounted upon the base I in a position such that the ion: gitudinal axis the member 2 lies substantially parallel to the plane of the base member I.

It will be understood that while the coil support 2 is generally cylindrical in form and hollow, it may have any convenient form which will permit movement 01 the core within the coil, and may be made of any suitable insulation material such as Mycalex. A pair of bearing members 4-4 are supported by bracket members 5-5 from the base I, said bearing members L4 being preferably axially aligned with the axis of the coil form 2. A core supporting rod 8 is slidably mounted inthe bearing members 4-4, said rod 8 having fixedly mounted thereon a core memher I. The core member I is dimensioned to be received within the hollow center of the coil sup port 2, the rod 6 being or a length suflicient to move the core I from the position shown in Fig. l, to a position in which it is fully inserted into the coil support 2. The rod 5 may be provided at one end with a suitable knob 13 to facilitate movement of the core member into and out oi the confines of the coil form 2.

The inductance winding 9 is wound upon the coil support 2 in a manner to be hereinafter more particularly described, said winding being provided with end terminals ill and a center or midtap connection I i.

It will be understood that the particular giforni or the coil support 2, the core member i, i

the particular means for shifting the core rosin her into and out of the coil support 2, may be varied within wide limits without crliicing l of the advantages accruing from the inven on,

and for this reason it will be appreciated that i do not limit myself to the particular i'crin of these elements shown in Fig. 1, but reserve the right to employ other forms of said ports and various mechanical expedient-s for shifting the core member longitudinally into out oi the inductance winding.

As previously indicated, I propose to provide inductance winding in which plural coil. sections are disposed to provide coincident magnetic fields in which a core member may be moved. I have illustrated in Figs. 2, 3 and 4, some approved forms of the inductance winding. Thus in Fig. 2 I show the winding in the form of a bifilar winding or helix comprising wires i2 and i3 wound side by side and in the same direction around the coil support indicated at 2. One end M of the wire or strand i2 is connected to one end it or the wire or strand 13 to form a center tap for a continuous winding comprising plural coil sections formed respectively by the wires or strands l2 and I3. The opposite ends of the respective wires or strands i2 and I3 form the end connections for the inductance unit and in practice will be connected to the end terminals ill or the unit as shown in Fig. 1, while the connected ends 14 assess? and II are connected to the center or mid-tap connection I! of said unit. A consideration oi this form of the winding will show that the coil sections formed by the wires l2 and I3 respectively are positioned upon the coil form or support 2 in a manner to provide coincident magnetic fields in which a core member such as 1, may be moved to simultaneously vary the inductances of said coil sections in the same amount.

In Fig. 3 I have shown a slightly diflerent modification of the arrangement 01 the coil sections on the coil support. In the arrangement shown in Fig. 3 the wires or strands I! and I! are started at points on the periphery 01' the coil form 2 angularly displaced degrees. The two wires i8 and Il however, are wound in the same direction about the support 2 and the end I! of the wire I8 is connected to the end IQ of the wire I! in a manner previously described to form a center tap connection, whereas the opposite end portions of the wires 18 and 11 are utilized for the end connections of the unit as previousiy described in connection with the iorm oi winding shown in Fig. 2. It will be realized that by arranging the windings in this form, there is absolute symmetry between the two windings and the core '1 in all positions of overlap between the core and the coil sections.

In both forms of windings as shown in Figs. 2 and 3, the coil sections on opposite sides of the center tap are connected in series aiding relation. This is desirable in certain types of con trol, and is essential where permeability tuning is employed. It is to be noted, however, that the same advantages in respect to simultaneously varying the inductance-s of the two coil sections in equal, amounts may be realized even though the two coil sections are connected in series bucking relation. This form of the inductance winding is shown in Fig. 4 where the two strands M and H are wound in opposite directions about the form 2 and wherein the opposite ends of the respective strands are ccizciiected as at 22 to :iorm the center tap come .on of the unit whereas the terminal. portions Eli and 24 provide end connections for the unit when made in iorm.

it will be appreciated that by arranging the coils in the manner suggested in 2 and 3, namely, in series aiding relation, the induce L oi the unit is greater than that of the helix wound with the same length of wire, wherethe quantity Con, Comrnnrsow Darn Bifilar coil as B767 Fig. 3

Winding-11 T. P. 1.

Double pitch thread 19 turns total Winding length=t%" Wire=#26 tinned copper Winding length=%" Number of turns=19 Wire is #26 plain enamel Form: .255" I. D. x .270" 0. D. Wound 22 turns per inch such as by liquid insulating coating applied to 2,808,807 3 Core outside of coil. Core outside of coil.

L=1.4p.h L1=,5,.h u-gm Lt=2.8p.h L1= '=2.1 n

L j h L8=L6Ih LB=L6ph M=.1p.h Core 'binserted 8 LIL-31'2"! Ll:

L'=2.4,i11 L1=.a,ln u=.4ni

- L:==.8uh L=3H h Li=La=2.4ph

La=l.6 h Ln=1.6ph M=.25 .h I Standard v1o LI=2Jph LI: 3M1, winding. Definition of terms used: 2 5 Pitch thread Lt=total inductance. ggg: g g H" La=Bridge residual inductance.

=Measured due :1 Wire=#26 tinned copper wire uaL in ta minus the ream Li=inductance of one section of the coil outside of from an open end to center tap.

L=1.1 h L1=.5 h M'=.05,uh =inductance of other coil section from L2=.5,uh opposite open end to center tap. Core inserted to center of 0 Some discrepancies appear in the measure- L=2L1 h L1=1A h M= 05,,h ments as shown, due to the impossibility of oper- L2: 911 ating the measuring apparatus with perfect acp curacy.

that th two coil sections may ice wound with any lively i fi Of the center mp in r respec o e we co sec ions disposed on oppoggg 9f i ig gg j iffifgggl m gfi i gf site sl des thereoL This isevident from the same j ggi ggi that shownemefig 3 inductance values for each coil section when the wherein the displacement is substantially 180 z 1s laser-ted Wlthm 5? @011 from ,g e es and th minimum being that shown in e f m o eommdent magmm figlds' g g; Qhere tmpd tart fmm Substantmn data alcove set forth shows that the coil sections a 13013146 is m gg m *he form 2 y have identical inductance values for the same m order show that' the inductance values prfmon whether the core member {35 aft-he two c011 Sammy, of the unit 10mg d as w thro the 0011 form or completely outside there-- Shown in Fig 2 are 512mm? tmuy identical even or. The data also shows clearly the advantage in though g strands stagt at Substantially thg respect to the increased values of mutual induct= a mint on the periphery of the con form 2 I ance to be realized by arranging the coils in series pi e 561 w W0 et of (ma rtaimn to iii aiding relation with the respective magnetic fields if 0 s pe g 0 thereof coincident. It is apparent that due to dinerent coils made in accordance with the wind= mm a Hi 0 1 ti f mg n t ing of Fig. 2. in both of these instances the two m re on o c0 Ions he Strands are Started at substantially the same mutual inductance adds to the total inductance point on the pfiflphery of the coil form the r and therefore results in a higher inductance for strands lying side by side and being wound ill-the a given number bums; Thus the 0115 may same direction. The strands of coil No. 1 were have fewer turns for glvenmductance' and a slightly spaced axially of the coil, whereas the smaller nd more compact unit results. strands in coil No. 2 were disposed in contiguous a The 0011 5601910115 y be mounted P the relation coil form in any convenient manner. Inas- Coil No. i much as it has been found that the most eitective form of the inductance unit for use Winding leugth= /e in permeability tuning is that form in which Number oi tums=l9 the respective strands lie parallel to one an- Wlre is 6 tinned canc r other throughout the length of the wind- Ffllmi Threaded 11 double m ing, I find it convenient to provide the coil form with a double spiral groove as shown in Fig. 5. Care l of The spiral groove may have any convenient or Lt=2 9Fh L1=L2=3m desirable pitch and. it serves to maintain the re- LR=1.6,I-lh LR=1J5ph M=.18,lh 80 Spective strands in thedeslred parallel relation- LEzlB'uh LE: 55 ship throughout the Winding without any other means or device for anchoring the convolutions or V2 inserted. of the winding. While I have referred to this form of coil support as a desirable form, it is of Lt=3.9 h Ll=Lz=3ph v course to be understood that it is not necessary i f-g g F to provide spiral grooves in the coil support, and E- that the full advantages accruing from the in- I vention may be realized by merely winding the Coil No. 2

- 7 strands on a conventional cylindrical form and anchoring them in position by any known means the windings while in place on the support.

It will be understood that the invention described is advantageous in any case where it is desired to simultaneously change the inductance: of branch circuits, by the movement or a single core member in the magnetic ileld of a tapped winding. and that be ferromagnetic, ior example a powdered iron core, or non-magnetic and electrically conductive, for example a core of copper or brass. depending upon the nature or inductance change desired to be produced by movement or the core member relatively to the windings of the inductance device.

In Figs. 6 to 9 inclusive, I have set iorth representative forms of networks including balanced branch circuits wherein the inductance unit oi the present invention may be used to great advantage. In each of the circuit diagrams I have shown the inductance units as a straight wound helix or inductance having a center tap and end connections, but it will be understood that in each instance the inductance unit is in substance one or the forms previously described as shown in Figs. 1 to 4 inclusive.

In Fig. 6 I have shown a typical plate neutralized single ended amplifier wherein the inductance unit of the present invention has the center tap connected to the source of B-battery potential, and the opposite end terminals of the unit are connected respectively to the plate and grid electrodes of a vacuum tube.

In Fig. 7 I have shown a typical example of a shunt fed push-pull amplifier or oscillator wherein the inductance unit of the invention has its mid -point grounded and the opposite end torminals thereof connected to the respective plate electrodes of the vacuum tubes.

In Fig. 8 I have shown a series tuned amplifier or oscillator in which the center tap of the inductance unit of the present invention is shown connected to the source of Bbattery potential through a pair of radio frequency coils inter connected with a condenser. The opposite ends of the inductance unit are connected to the respective plate electrodes of a pair of vacuum tubes.

In Fig. 9 there is shown a conventional form of series fed amplifier or oscillator in which the inductance unit of the present invention is shown with its mid-point connected to the source of B-battery potential and its opposite end terminals connected to the plate electrodes of a pair of vacuum tubes.

It should be noted that while the circuit diagrams of Figs. 7 to 9 inclusive, show the inductance unit of the present invention connected to the plate electrodes of the respective tubes, the inductance unit may be connected to the grid circuits of the tubes if desired.

In Fig. 10 I present a chart showing possible connections and results with inductance devices as described above in connection with Figs. 2, 3 and 4. Two conditions of winding are illustrated, first the condition of winding in which the coil sections are parallel wound, and second, the condition of winding in which the coil sections are reversely wound. In the first vertical column of the chart, the coil type is designated, each different connection of the windings of the inductance device being considered to be a different type for the considerations of the ,chart. The second vertical column indicates whether the coil sections or windings of the inductance device are parallel wound or reversely wound. The third vertical column indicates the end terminals of the inductance device by reierence to the amsaid core member may either aaoaesv propriate diagrammatic drawings of the device at the top of the chart, and the fourth vertical column indicates the manner of forming the center tap connection by reference to saiddiagrammatic' drawings. The fifth vertical column indicates whether the relation of the coil sections or windings is aiding or bucking for each or the coil types, and the sixth vertical column illustrates schematically the corresponding eflect oi inductance change for a single layer solenoid, resulting from the insertion of a core into the wind ings of the inductance device of the corresponding type coil, together with the locations in the solenoid at which said inductance changes take place, if it were possible to produce such inductance changes in connection with single layer solenoids.

A consideration of the results secured by ditferently connecting the coil sections or windings of the inductance device, to produce the different coil types illustrated in the chart 01'. Fig. 10, shows that the portions of the coil sections or windings directly affected by the insertion of a core, are determined by the manner of connecting the terminals of the coil sections; and it also appears that the aiding or bucking relationship of the coil Sections or windings to each other is determined by whether said sections or windings are parallel wound or reversely wound, in conjunction with the manner in which the connections of the coil sections or windings are made, it being possible to obtain the same inductance distribution with either an aiding or a bucking relationship of the coil sections or windings, in any case.

From the foregoing examples of the manner in which the inductance unit oi the present invention may be employed, it is apparent that the unit lends itself admirably to instances in which permeability tuning is desirable or necessary for simultaneously tuning balanced branch circuits of a network. It is of course to be understood that condensers connected in shunt relation across the units as shown, may be employed to assist in control of the branch circuits if desired without in any way interfering with the efiec tiveness of operaton oi the respective inductance units. I

The center tapped bifllar inductance unit or the present invention has been designed especially for use in permeability tuning systems employed in radio transmitters and receivers, and has been used eifectiveiy within a wide range of frequencies, including frequencies as low as 2.9 megacycles up to frequencies as high as 200 megacycles.

It will be understood from the foregoing description that the present invention difiers from known inductance units including conventional center tapped solenoids and/or bifilar windings, in that the present inductance unit is characterized by coil sections disposed to provide coincident aiding magnetic fields within which a single core member may be moved to simultaneously vary the inductances of the coil sections. While I have referred herein to a core member of powdered iron, it is of course to be understood that the invention is not limited to a core of this form, and that any known or convenient means may be employed for shifting the core with respect to the coil form.

While the invention is described in connection with the particular embodiments above set forth, it will be understood that the invention includes equivalent structures involving the principles of operation described, which are included within the scope of the appended claims.

Having thus described my invention what I claim is:

1. In a network including a pair of tunable branch circuits, an inductance unit comprising a winding defining two coil sections having substantially identical electrical characteristics and disposed to provide substantially coincident fields, means connecting one of said coil sections in each branch circuit with the coil sections in series relation, an inductance-changing core member common to both coil sections, and means for adjusting said member with respect to said coil sections to simultaneously tune said branch circuits to the same resonant frequency. v

2. In a network including a pair of tunable branch circuits and a, pair of electron tubes connected in push-pull relation by said branch circuits, an inductance unit comprising a winding defining two coil sections having substantially identical electrical characteristics and disposed to provide substantially coincident fields, means for connecting one of said coil sections in each branch circuit with the coil sections in series aiding relation, an inductance-changing cpre member movable in said coincident fields, and means for adjusting said core member within said fields to simultaneously tune said branch circuits to the same resonant frequency.

3. In a network including a pair of tunable branch circuits and a pair of electron tubes connected in push-pull relation by said branch circuits, an inductance unit comprising a bifllar winding defining two coil sections constituting the inductive portion of said unit, said sections having substantially identical electrical characterstics, means connecting one of said coil sections in each branch circuit with the coil sections in series aiding relation, a capacity unit in shunt relation to said coil sections, an inductancechangng core member common to both coil sections, and means for adjusting said core member axially witlrrespect to said coil sections to simultaneously tune said branch circuits to the same resonant frequency.

4. In a network including a pair of tunable branch circuits and a pair of electron tubes connected in'parallel relation by said branch circuits, an inductance unit comprising a winding defining two coil sections having substantially identical electrical characteristics and disposed to provide substantially coincident fields, means connecting one of said coil sections in each branch circuit with the coil sections in serie aiding relation, an inductance-changing core member common to both coil sections, and means for adjusting said core member axially of said coils to simultaneously tune said branch circuits to the same resonant frequency.

5. In a network including a pair of tunable branch circuits and a pair of electron tubes connected in push-pull relation by said branch circuits, an inductance unit comprising a winding constituted by helical coil sections connected respectively with said branch circuits and disposed to provide substantially coincident fields, said coil sections being connected to form a tap connection of said winding, the turns oi one coil section being adjacent throughout to the turns of the other of said coil sections, and an inductance-changing core member common to said coil sections and adjustable relatively thereto to simultaneously tune said branch circuits to the same resonant frequency.

GEORGE B. McCLEL-LAN. 

